Internal combustion engines are commonplace in society, especially, for example, in automobiles. A typical internal combustion engine works by filling a combustion chamber in an engine with air and gasoline, compressing the air and gasoline, igniting the gasoline, and emitting exhaust from the chamber. Because internal combustion engines generate a lot of heat, the engines must include a cooling system to keep the engine from overheating. If the cooling system of an engine does not cool the engine sufficiently, the temperature of oil in the engine will rise and moving parts in the engine can become stuck. This is called oil caulking.
A lecture article for a mechanical engineering academic society, No. 96-1, titled “Combustion and combustion chamber of heat shield engine” was published in 1996. That article teaches that when a piston using a heat insulator, such as ceramic, is applied to a gasoline engine, the temperature of the heat insulator becomes high due to a heat accumulation effect of the heat insulator when the engine is operating at full load. The temperature of a groove portion for a piston ring, which is located within a small distance from the piston crown surface, also increases. Therefore, the piston ring can become stuck due to oil caulking. Specifically, the piston ring becomes incapable of freely moving because a portion of adhering oil is carbonized and gradually fills, or caulks, the piston ring groove.
Accordingly, a need exists for a thermally insulated engine. Specifically, there is a need for a thermally insulated engine in which the engine thermal efficiency is improved, which thereby reduces the cooling loss and prevents oil caulking.